This renderer reads a `[svn:externals]` section in the TracIni, which looks like this:
{{{
[svn:externals]
http://ourserver.ourdomain.com/svn/eng-soft http://localhost:8000/devel/browser/tags/$path?rev=$rev
svn://dserver/support_repository http://dserver/trac/support/source/$path?rev=$rev
}}}
That way, the configured `svn:externals` entries will link to the right place in other Trac (but the URL can point to other servers, like ViewVC or directly in the Subversion server through the http: protocol).
